One of the interesting things about disaster recovery planning for nuclear power plants is that you count on (X) number of things to go wrong and figure out how the plant recovers gracefully. In Japan they've effectively had three things go wrong: earthquake, tsunami, and general infrastructure damage. Most disaster scenarios only cover a single event and TEPCO has a lot to deal with.

In a disaster scenario the first reactions are generally passive (dropping of control rods, changing where water flows) and then "all" that remains is to cool the decay heat. Aye, here's the rub: the cooling system is not a passive system. It requires power to drive the water pumps for the cooling system that siphons the heat away from the reactor vessel. After initiating reactor shutdown the most critical time period is the first little while as that is when there is the most heat. Too much heat and it'll damage the fuel, vessel, and/or the cooling system and can effectively damage the reactor enough so to prevent it from ever recovering (thus, meltdown).

The questions left to ask are to what degree the cooling systems (primary and backup) are working, and whether they've been powered consistently. With that bit of information alone we'd be able to make a pretty accurate estimate as to the state of the reactors in question. What is scary is that it would be really simple to say that all of those systems are working as expected and that there is nothing to worry about. Since that hasn't been said I'm of the opinion that there is definitely something to worry about.